Stimulation of iodide uptake by human chorionic gonadotropin in FRTL-5 cells: effects on sodium/iodide symporter gene and protein expression

Abstract

Background: Various clinical and experimental findings support the concept that human chorionic gonadotropin (hCG) can stimulate iodide uptake in thyroid cells.

Design: We investigated the molecular mechanisms underlying the effects of hCG on iodide uptake, and particularly its action on the expression of Na+/I- symporter (NIS) mRNA and protein.

Methods: Iodide uptake was analyzed in FTRL-5 cells by measuring (125)I concentrations in cells after a 30-min exposure to 0.1 microCi carrier-free Na (125)I in the presence or absence of hCG or, for control purposes, TSH. Expression of NIS mRNA and NIS protein synthesis were evaluated, respectively, with a semiquantitative 'multiplex' RT-PCR method and Western blot analysis.

Results: Iodide uptake was increased by hCG in a dose- and time-dependent manner: maximal effects were observed after 72 h of stimulation. The effect was cAMP dependent and paralleled that of TSH, although it lacked the early cycloheximide-independent component seen with TSH, and its peak effect was lower. Semiquantitative multiplex RT-PCR revealed that hCG produced a significant increase in NIS mRNA levels that was detectable after 4 h and peaked after 48 h. In contrast, in TSH-stimulated FRTL-5 cells, maximum NIS mRNA expression was observed after 24 h of stimulation. Western blot analysis demonstrated that hCG also caused a 2.5-fold increase over basal values in NIS protein levels, which was similar to that observed after TSH stimulation although the peak effects of the latter hormone were less marked and occurred earlier.

Conclusion: Our data demonstrated that hCG stimulates iodide uptake in FRTL-5 cells by increasing NIS mRNA and protein levels. Thus, the functional status of the thyroid may be influenced by hCG-dependent changes in NIS expression occurring during pregnancy.